frequency-modulated automotive lidar · •pulsed lidar systems do not simultaneously measure range...
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© Copyright 2018 Xilinx
Frequency-Modulated Automotive Lidar
Jim Curry
VP of Product
Blackmore Sensors and Analytics, Inc.
© Copyright 2018 Xilinx
FMCW Measurement Theory
Pulse BWDetector BWDigitizer BWPeak Power
Limiters to rep rate, resolution, and range
Optical Bandwidth
Electronic Bandwidth
Peak Power
FMCW Uncouples Traditional System LimitationsMost 3D lidar systems are pulsed, “direct detect” based.
Flexible and adaptive technique which provides compelling advantages
trep
Pow
er
Time
Direct Detection
trep
Pow
er
Time
Heterodyne Detection = FMCW
Op
t.
Fre
q.
Time
Up Chirps
Constant Power / Frequency Modulated
Superior Resolution, Dynamic Range,
Single-Photon Sensitivity
Doppler MeasurementMulti-Return Resolution
Eye SafetyLow Cost
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FMCW Measurement Theory
LO RX
Op
tica
l Fre
qu
en
cy
Time
𝑓𝑏 = 𝜅𝜏𝐷
𝐵
The properties of light are leveraged to make a physically superior measurement
FFT to get“range profile”
Po
we
r (d
B)
Range
Δ𝑅 =𝑐
2𝐵
The optical bandwidth, B, can be increased electronically to meet nearly any resolution
requirement
𝑓𝑏
𝜏𝐷
Result is a beat note with frequency 𝑓𝑏that is digitized and processed.
Splits closelyspaced targets
The LO/RX mixing process is optical.
The beat note is measured, not the RX signal directly.
Shot-noise floor of the LO(very stable!)
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No Compensationw/ Doppler Compensation
Doppler ChallengesStatic Imaging of Trees, Slight Breeze
In the infrared band, Doppler shifts are ~1MHz per m/s. This is very challenging to deal with compared to radar (~1kHz per m/s).
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Simultaneous Range and Velocity
StationaryApproaching Receding
• Pulsed lidar systems do not simultaneously measure range and velocity
• Radar systems measure velocity but have poor spatial resolution
• Coherent (FM) lidar combines high-resolution spatial and velocity measurements
• For perception, instantaneous velocity is very valuable‒ Faster and more accurate scene segmentation
‒ Velocity content of tracked objects helps classify them (micro-doppler signatures)
5
+3.5m/s -3.5m/s
Illumination Direction
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Simultaneous Range and Velocity
6
StationaryApproaching Receding
+3.5m/s -3.5m/s
Illumination Direction
6
150m
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Interference Rejection
• AM lidar pulses look exactly the same• Lidar-to-lidar interference cited as a
“pain point”
• Sunlight elevates noise floor of AM measurements, reducing lidar sensitivity in the daytime
• Blackmore’s FM lidar operates interference-free• No issues with sunlight
• No issues with other cars’ sensors
• No issues with self-interference
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Long-Range Performance
Sensor Location
In-N-Out Burger Sign
Structure @ 400m
Gives autonomous systems plenty of range for smooth braking
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A Scalable SolutionTechnology leverages semiconductor foundries
+
Low-power continuous-wave laser compatible with integrated photonics, including optical phased arrays
Non-Mechanical
Beam Scanning
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E
Example FM automotive lidar data
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Single-pass mappingHeight (Altitude) ColorationOne pass in one direction
One pass in each direction
Moving points stripped out using velocity field
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High-Speed Performance
Performance Maintained at Highway Speeds
Height (Altitude) ColorationMoving Points Removed
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Point-by-Point Velocity
Direct velocity measurement enables segmentation and tracking
of moving objects
Foot trafficVelocity Coloration
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Motion-compensation of velocity dataMicro-doppler data reveals wheel-spin
Precise, high-dynamic range velocity data
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Questions?
Height (Altitude) ColorationReflectivity Shading
• No saturation or blooming artifacts from bright reflectors
• Extremely high damage threshold• Easily measures reflectivity differences from
pavement markings
High-Dynamic-Range Reflectivity Data
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High Spatial Precision
Enables detection of even minor pavement defects
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See through, detect, and identify obscurants
Velocity coloring. Grey points=water surface, colored points=mist
Thin layer of suface mist over pool
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Wing-Walk in Doppler FieldQuestions?Jim CurryVP of ProductBlackmore Sensors and Analytics, [email protected]